In conventional electrophotographic printer, a photosensitive drum that has been charged is irradiated with a light source to form an electrostatic latent image, toner is made to adhere to the electrostatic latent image for development, and the toner image is transferred to a recording medium.
The electrophotographic printer is capable of printing a page at a time, so that it can be used as a page printer.
FIG. 10 is a functional block diagram showing a conventional printing apparatus of this type.
As illustrated, a host computer 2 is connected to a printing apparatus 1 via a parallel interface or a serial interface, generating print data, and supplying the print data to the printing apparatus 1.
When the print data is supplied from the host computer 2, the printing apparatus 1 performs reception processing (step S1), editing processing (step S2), development processing (step S3), and reading processing (step S4), to produce dot image data, and sends the dot image data to the printing section 3 of the electrophotographic printing system.
In the reception processing S1, the print data that have been received are in the form code data such as "ESC(8U" (signifying designation of symbol set Roman-8); "ESC & K10H" (signifying character pitch 10 characters per inch); "LED PRINTER IS" (character series); . . . "CR LR" (signifying carriage return and line feed). These data are stored in a reception buffer, not shown.
In the editing processing S2, the code data that are stored in the reception buffer are read out and converted into intermediate codes, and arrangement is made, e.g., as shown in the figure, a character code series "LED PRINTER is high quality . . . " starts at the point (x=0, y=0), Y=0-th dot, another character series "Advantages of page . . . " starts at the point x=0, y=20), and a further character series starts at the point (x=10, y=50). In addition, the sizes and typefaces of the print characters are designated by Font=3 or Font=5.
In other words, the editing is due so as to facilitate development into bit-map data in the subsequent development processing step S3, and the edited data are stored in a page memory, not shown.
In the development processing S3, designated font patterns are read from a font memory 4 in accordance with the intermediate codes in the page memory, and written into the designated locations in a raster buffer 5.
In the reading processing S4, the dot pattern data having been written in the raster buffer 5 are read by raster scan, and converted by a shift register 6 from parallel data into serial data, and the data are then sent to the printing section 3. The raster buffer 5 has a memory capacity for printout of one page, e.g., about 1 Mbytes in the case of a page of letter size with a density of 300 dots per inch. The raster buffer 5 is either of the full-page buffer type in which reading is effected after development of data of one entire page is completed, or of the band-buffer type in which the limited memory capacity is divided into an area for dot pattern development and an area for reading, and these areas are used alternately for development and reading of one page.
In the above conventional printing apparatus of the full-page buffer type, memory capacity for one page is needed, so the memory capacity required is large. This increases the cost of the printing apparatus, particularly of those having a higher print dot density.
In the case of the band-buffer type, when it is necessary to write a dot pattern at the border of the raster buffer 5, part of the dot pattern 5 that has overflown the page must be written again in the next cycle. This will impose a limitation to increasing the writing speed. Where complicated patterns and a multiplicity of character patterns are concentrated in a specific region, the writing of the dot patterns is slower than the printing.